The present invention relates to a novel multicore optical fiber suitable for high density optical communications and more particularly to a multicore optical fiber such as a tape-shaped optical coated fiber equipped with a covering layer which is capable of effectively protecting each optical fiber element and is easy to handle when such optical fibers are coupled together.
With the recent advances in data communications, there has been a requirement for signal transmission at higher speed. As an example of materialization of such high speed signal transmission technology, the recent practical use of optical communications can be cited. The optical signal transmission has many advantages from the standpoint of communications in that the property of light itself is utilizable for realizing high speed transmission and that optical fibers used as transmission lines are lightweight and little affected by magnetic or electric fields. However, an optical fiber is still required which will increase the capacity of signal transmission and, there have been various kinds of optical fibers for signal transmission proposed.
A multicore optical fiber is one of the proposed optical fibers for such circumstances. The multicore optical fiber, which is formed by integrating fiber elements as optical waveguides with a covering layer common to them, is now spotlighted as being of realizing high density signal transmission with simple care in handling.
FIG. 1 is a sectional view showing the typical structure of a multicore optical fiber of the sort aforementioned, wherein glass fibers 1 for optical transmission respectively covered with covering layers 2 are further equipped with a common covering layer 3 to form a tape-shaped optical coated fiber.
In the prior art, the covering layers 2 and 3 are formed of, for example, ultravoilet-curing urethane acrylate.
When the multicore optical fiber is coupled to another member, e.g., an ordinary single core optical fiber or another multicore optical fiber, however, the form of a tape is difficult to handle and further the problem of transmission loss resulting from the connection of both also arises. In consequence, the common covering layer 3 must be removed to handle each element.
On the other hand, the glass fibers without the covering layer suffer from insufficient strength and may break. Thus, when each element is a handled, it is prerequisite to remove the common covering layer 3 of the multicore optical fiber in such a manner that the covering layer 2 of each element perfectly remains as it is and is also undamaged.
In the case of the conventional multicore optical fiber, however, the covering layers 2 and the common covering layer 3 are made of the same material. Even if they are not bonded chemically but bonded merely under pressure, it is not possible to remove only the common covering layer 3 while the covering layer of each optical fiber is left unremoved completely.
High degree of skill and many workhours have been required to couple multicore optical fibers.
Another known arrangement is to form a covering layer 2 of thermosetting silicone resin on each optical fiber 1 and then form a covering layer 3 of nylon common to the optical fibers, in order to provide a multicore optical fiber. The operation of removing the common covering layer 3 from the multicore optical fiber of that type is considerably easy because the covering layer 3 is relatively readily peeled off the covering layers 2.
However, because the mechanical strength of the thermosetting silicon resin used for the covering layer 2 of the optical fiber thus constructed is extremely low, the covering layer of each optical fiber element after the removal of the common covering layer can not withstand rubbing or scratching and are thus unsuitable for practical use.
The normal way of removing the common covering layer 3 of the conventional multicore optical fiber is, for instance, to vertically tear the common covering layer 3 into two pieces from both left- and right-hand ends A, A' with respect to the section shown in FIG. 1. However, the thickness of the common covering layer 3, excluding its portions respectively penetrating into the gaps between the optical fiber elements 1 and the covering layers 2, is practically uniform and therefore the common covering layer 3 will not readily be detached by simple pulling the halves thereof in certain directions. Even if it is attempted to tear the common covering layer into two pieces from cut points made in the edges thereof with a knife and the like, the common covering layer is not always torn in the longitudinal direction of the optical fiber. The removal of the common covering layer of the multicore optical fiber is indeed troublesome work.